Mechanical interlock for servo motors



NOV. 20, 1934. L TOBlN MECHANICAL INTERLOCK FOR SERVO MOTORS Filed March 6. 1954 INVENTOR.

Patented Nov. 20, 1934 UNETED STATES MECHANICAL INTERLOCK FOR SERVO MOTORS Arthur Little Tobin, Lynnfield Center, Mass, as-

signor to Ruggles-Klingemann Mfg. 00., Salem,

Mass.

Application March 6, 1934, Serial No. 714,350

7 Claims.

My invention relates to servo motors of the fluid pressure type, and more specifically to means for insuring the operation of such motors in the r quired sequence.

Servo motors of the duplex type are employed in the operation of valves and dampers for the control of fluids and gases where it is required to effect operation a definite sequence. One example is in the control of combustion in steam boilers in which both forced and natural draft are used, the purpose being to first apply natural draft on light boiler loads and to shift to forced draft as the boiler load increases. Another example is in process work such as paper drying, in which both exhaust and live steam is required to be controlled in the proper sequence. In such cases the operation of the servo motors is usually automatically controlled either from temperature or pressure.

In the application of servo motors it is sometimes found desirable to use twin motors, and to have one of these motors operate its entire stroke in one direction before the other motor commences to act, and to have the last motor to com plete its full stroke and return to its initial position before the first motor is returned to its starting point. As it is more convenient to control such twin motors from a single control unit, it becomes necessary to provide some means to insure the operation of such motors in the required sequence.

Various methods have been adopted to insure this result, such as weighting one of the plungers to cause the lighter plunger to act first. Also by making one of the cylinders larger in diameter than the other, so it will act on a lower pressure and, consequently, act first. But, such arrangements are not entirely satisfactory for the simple reason that the load which the plungers operate, is not always uniform for each plunger, and consequently, such methods of securing sequence of control are always unreliable. For this reason, I have devised positive mechanical interlock for such motors which very effectively overcomes these defects.

For a more complete disclosure of my invention, reference should be made to the following specification and drawing.

The drawing shows a vertical elevation of twin servo motors, certain parts being in section. A control valve (1) has inlet for fluid pressure at (2) exhaust to atmosphere (3) and delivery connections (4) and (5). When in the position shown, fluid pressure is admitted to the bottom cylinders (6) and (7), and the upper end of cylinders (6) and (7) above pistons (8) and (9), is open to the atmosphere through conduit (10). When the control valve is operated to the position shown by dotted lines of the lever (11), the inlet for fluid pressure will then be to the top of so cylinders (6) and (7) and the bottom below pistons (8) and (9) will be open to the atmosphere.

It will be understood that pressure admitted at the bottom connectionnot only comes directly under piston (8) but also passes through port and exerts an equal pressure on piston (9) Likewise, pressure admitted at the top connection passes through port, and consequently, exerts an equal pressure on the upper side of both pistons (8) and (9). 7'0" Pistons (8) and (9) have piston rods (13) and (14) which pass through stufling boxes (15) and (16) in cylinder cups (17) and (18).

To the top of these piston rods is attached side V bars (19) and (20). These side bars are guided V5 in a T slot bearing on their respective cylinders.

I will now explain my novel mechanical interlocking arrangement. A roll (21) is held in engagement with side bar (19) by spring (22). A plunger (23) extends through a hole in the 8G- plunger casing and engages a notch (29) in the side bar (20). Roll (24) which is normally pressed against side bar (29) by spring (25), has a plunger (26), but due to the fact that roll (as) is in a depression (30) on side bar (20), the plunger (26) is free from engagement with side bar (19). Assuming that fluid pressure is now admitted to the under side of pistons (8) and (9), it will be seen that piston (8) is free to move upward, carrying with it piston rod (13) 9c and side bar (19), but that piston (9) is locked in its present position due to the fact that plunger (23) is held in the notch (29) on side bar (20). When side bar (19) which is attached to piston (8) reaches an upward position where depression (27) is opposite roll (21) spring (22) will force roll (21) to the bottom of depression (2'7), thereby releasing plunger (23) from the notch (29) in side bar (20).

Y Piston (9) is now free to move upward, and as notch (28) in side bar (19) is now opposite plunger (26) consequently, as roll (24) is forced out of its depression by theupward movement of the side bar (20) plunger (26) is forced into engagement with notch (28), thus insuring piston (8) against further movement until such time as piston (9) has completed its upward stroke, and has returned to its initial position as shown in the drawing. After piston (9) has returned to its initial position, it automatically unlocks side bar (19) and allows piston (8) to also return to its initial position, and both pistons and looking devices will then be as shown in the drawing.

It will now be seen that by the operation of the control valve (1), these twin motors independently operated from a single control element, one motor making a complete upward stroke at which point the second motor is released and the first motor locked against further operation, has made its upward stroke, and returned to its initial position. It will be understood that my novel mechanical interlock for a servo motor can be arranged for other sequences of operation, other than that above described. I therefore limit myself only to the scope of the appended claims.

1. Mechanical interlock for servo motors, comprising two parallel movable members operated by said motors, each member having a locking notch and a co-operating releasing depression on the opposite member, two spring operated plungers, one of said plungers'engaging a locking notch on one of said movable members and to be released by spring tension when engaging the depression on the other movable member, at which time the other plunger is forced into the locking notch on the last named movable member by the operation of the first named movable member.

2. Mechanical interlock for servo motors, comprising two parallel movable members operated by said motors, each member having locking notch and co-operating releasing depression on the opposite member, two spring operated plungers, one of said plungersengaging a locking notch on one of said movable members and to be released by spring tension when said plunger engages the depression on the other movable member, at which time the other plunger is forced out of the depression on the first named movable member by the movement of said memberyand engages the notch on the second named movable member.

'1 movable members operated from said piston rods,

of said pistons against movement when subjected each member having a locking notch and a oooperating releasing depression on the opposite member, two spring operated plungers, one of said plungers engaging a locking notch on one of said movable members and to be released by spring tension when engaging the depression on the other movable member, at which time the other plunger is forced into the locking notch on the last named movable member by the operation of the first named movable member.

'4. Mechanical interlock for servo motors, comprising two cylinders having pistons and piston rods operable therein in two directions by fluid pressure, controllingmeans for admitting fluid pressure to either side of each of said pistons, and for releasing pressure from the opposite side of each of said pistons, means for locking one to fluid pressure untilthe other piston has comone or the other direction, locking means 00- operating with said movable members for holding one of said motors against operation when subjected to said source of power until the other motor has completed its limit of operation in one direction, at which position the said means releases the first named motor, and a second locking means operated by the operation of the first named motor for holding the second named motor against a reverse operation until the first named motor has completed its limit of operation in one direction and returned to its starting position.

6. Mechanical interlock for servo motors comprising two cylinders each having a piston operable therein, controlling means for applying a source of power to, each of said pistons simultaneously to operate said pistons in either one or the other direction, means including a piston rod for connecting said pistons to the device to be operated, locking means connected with said piston rods for holding one of said pistons against operation when subjected to said source of power until the other piston has completed its limit of operation in one direction, at which position said locking means releases the first named piston, and locking means for holding the second named piston against furthenoperation until the first named piston completes its operation in one direction and returns to its initial position.

7. In a mechanical interlock for servo motors, comprising 'two cylinders having pistons operable therein in either of two directions, a control valve having conduit connections for supplying a source oi pressure common to either end of both cylinders and for ventingthe opposite end of said cylinders, piston rods connecting with said pistons and extending through one end of said cylinders, a locking bar connect- "ed with each of said piston rods and arranged substantially parallel with the axis of said cylinders, two spring operated plungers mounted on said cylinders and located between said looking bars, said plungers being biased by spring in opposite directions and in contact with their respective actuating locking bar, each of said locking bars having a locking notch and a releasing depression, the arrangement being such that when either of said plungers are'forced into the locking notch on one of said bars, the other plunger will be held in the depression on the same bar thereby permitting only one of said pistons to operate at a time.

ARTHUR LITTLE TOBIN. 1 

